Aluminum-alloy composite suitable for anodization

ABSTRACT

An article comprises a bulk layer of an aluminum-alloy composite and a surface layer. The bulk layer comprises an aggregate dispersed in an aluminum-alloy matrix, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix, and having an average particle size of 100 microns or less. The surface layer comprises an anodized form of the bulk layer.

BACKGROUND

Aluminum alloys are strong, lightweight, easily formed, and easily machined. Accordingly, numerous products are made from aluminum alloys. Some aluminum alloys offer yet another advantage for consumer-product manufacture—namely, that the surface of the formed aluminum-alloy component may be further conditioned via the electrochemical process of anodization. Under suitable conditions, anodization of a formed aluminum-alloy component yields a smooth, wear-resistant, and visually appealing surface.

SUMMARY

Examples are disclosed that relate to strengthened aluminum-alloy composite materials and associated methods of manufacture. One example provides an article comprising a bulk layer of an aluminum-alloy composite and a surface layer. The bulk layer includes an aggregate dispersed in an aluminum-alloy matrix, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix, and having an average particle size of 100 microns or less. The surface layer comprises an anodized form of the bulk layer.

Another example provides an article formed from an aluminum-alloy composite, the article comprising a bulk layer of the aluminum-alloy composite and a surface layer. The bulk layer includes an alumina-powder aggregate dispersed in an aluminum-alloy matrix, the alumina-powder aggregate having an average particle size of 20 microns or less. The surface layer comprises an anodized form of the bulk layer.

Another example provides a method of manufacture of an aluminum-alloy composite article, the method comprising melting an aluminum alloy; dispersing an aggregate in the melted aluminum alloy to form a dispersion, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix and having an average particle size of 100 microns or less; cooling the dispersion to below a solidification point of the dispersion to form an aluminum-alloy composite; extruding the aluminum-alloy composite to form an aluminum-alloy composite extrusion; and anodizing the aluminum-alloy composite extrusion.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows aspects of example electronic devices comprising a hardened aluminum-alloy article.

FIG. 2 illustrates an example method of manufacture of an aluminum-alloy composite article.

FIG. 3 shows aspects of an example aluminum-alloy composite article.

DETAILED DESCRIPTION

This disclosure is presented by way of example and with reference to the drawing figures listed above. Components, process steps, and other elements that may be substantially the same in one or more of the figures are identified coordinately. It will be noted, however, that elements identified coordinately may also differ to some degree. It will be further noted that the figures are schematic and generally not drawn to scale. Rather, the various drawing scales, aspect ratios, and numbers of components shown in the figures may be purposely distorted to make certain features or relationships easier to see.

As noted above, high-strength, lightweight articles may be formed from various aluminum alloys. In some areas of manufacture, there is ever-increasing demand to further improve the strength-to-weight ratios of aluminum-alloy components. The demand is particularly evident in the manufacture of consumer-electronics. Laptop computers, tablet computers, and cell phones, for example, typically comprise a rigid shell or armature formed from an aluminum alloy. As the demand for display size in these devices continues to increase, it becomes necessary to engineer structural components from intrinsically stronger materials, in order to keep the weight of the devices within an acceptable range.

Table 1 shows the tensile strength of various aluminum alloys, along with certain other properties.

TABLE 1 Strength of selected aluminum alloys alloy temper tensile strength/ksi yield strength/ksi 5005 O 18 6 H12 20 19 H14 23 22 H16 26 25 H18 29 28 H32 20 17 H34 23 20 H36 26 24 H38 29 27 5050 O 21 8 H32 25 21 H34 28 24 H36 30 26 H38 32 29 5052 O 28 13 H32 33 28 H34 38 31 H36 40 35 H38 42 37 5056 O 42 22 H38 60 50 5182 O 40 21 H32 41 22 H34 48 37 H36 51 42 H38 54 47 6061 O 18 8 T4 35 21 T6 45 40 7075 O 33 15 T6 83 73

The 5xxx- and 6xxx-series aluminum alloys are popular choices for structural and enclosure components of consumer-electronics devices, due in part to their malleability, ductility, and ease of extrusion. For instance, the shell of a laptop computer may be cold formed from a thin, rolled sheet, or machined from an extrusion. A sheet of a 5xxx- or 6xxx-series aluminum alloy may be suitable for this application, when rolled to a thickness of 500 to 1000 microns (μm) or greater. When rolled thinner, however, the sheet may lack sufficient strength.

It will be noted, based on the Table above, that certain alloys of 7xxx-series aluminum may be significantly stronger than those of the 5xxx- or 6xxx-series, and may be used to make rolled sheets or extrusions of suitable strength, even when the thickness is 1 millimeter (mm) or lower. However, 7xxx-series aluminum may be disadvantageous for some consumer-product applications, as these alloys may be poor substrates for electrochemical anodization. In many instances, an anodized surface finish is desirable for structural components of a consumer-electronics device. Under suitable conditions, anodization of a formed aluminum-alloy component yields a smooth, wear-resistant, and visually appealing surface. However, anodization of a 7xxx-series aluminum article may cause numerous surface defects (cosmetic and otherwise), and may result in an overall low product yield.

Accordingly, examples are disclosed that relate to strengthened aluminum-alloy composites based on 5xxx- and 6xxx-series aluminum alloys, which may reliably provide substantially defect-free surfaces under electrochemical anodization conditions. As described in more detail below, a suitably strong, anodizable material may comprise an aluminum alloy composite in which a continuous alloy matrix is interrupted by a dispersion of small, materially hard particles, which are insoluble in the alloy. Without tying this disclosure herein to any particular theory, the strengthening effect may be somewhat analogous to the effect of precipitation hardening in conventional metallurgy, wherein the dispersion of insoluble particles limits the movement of dislocations within the alloy matrix, therefore strengthening the material. A disadvantage of precipitation hardening, relative to the approach here disclosed, is that if precipitates were to separate from the solid solution as large particles (due to slow cooling), the strengthening effect on the aluminum alloy may be limited. Similarly, if large precipitate particles fail to re-dissolve in the solid solution during solution treatment, the hardening effect may be minimal. On the other hand, if large precipitate particles did dissolve in the solid solution during solution treatment, but the holding time were too long, grain growth would be inevitable, which may result in lower strength and in discoloration after anodization.

FIG. 1 shows examples of various electronic devices that may include an aluminum-alloy composite article, as described herein. In particular, the drawing shows a laptop computer 10, a tablet computer 12, and a cell phone 14. Each of these devices may include a shell or armature made of hardened aluminum, which is extruded, and/or rolled, machined, and/or formed, and subsequently anodized. It will be noted, however, that this disclosure is not limited to such articles, but extends equally to the manufacture of various other hardened aluminum products—tennis racquets, bicycle frames, automobile components, or virtually any other hardened aluminum article.

FIG. 2 illustrates an example method 16 of manufacture of an aluminum-alloy composite article. At 18 of method 16, an aluminum alloy is melted in a crucible or other suitable container made of a refractory material. In some examples, the aluminum-alloy may include a 5xxx- or 6xxx-series aluminum alloy, although other aluminum alloys and unalloyed aluminum may be used in other examples. The temperature of the melt may be about 600 to 680° C., where aluminum and most of its alloys are liquefied, but the various refractory materials remain solid.

At 20 of method 16, an aggregate is dispersed (i.e., substantially uniformly mixed) into the molten aluminum alloy to form a dispersion. In general, the aggregate selected for dispersion may be a solid which is unreactive in the melt. In some examples, the aggregate added to the molten aluminum alloy may comprise 1 to 20 percent by mass of the aluminum-alloy composite. Compositionally, the aggregate may include a carbide, nitride, or oxide in the form of a freely flowing powder. In more particular examples, the aggregate may include alumina powder of any suitable mesh size. The average particle size of the aggregate may be 100 microns (μm) or less, 20 μm or less, 10 μm or less, 5 μm or less, or 1 μm or less, for instance. The morphology of the aggregate particles is not particularly limited, but may include substantially spherical or oblong particles. In some implementations involving subsequent extrusion, particles with very high aspect ratios (e.g., elongate fibers) may be avoided.

At 22 of method 16, the dispersion is cooled to below its solidification point to form an aluminum-alloy composite. Cooling may be accomplished rapidly, in order to avoid or limit separation of the dispersed aggregate from the aluminum alloy matrix.

Subsequently, in method 16, the aluminum-alloy composite may be extruded or optionally rolled. If extrusion is selected, then at 24, an aluminum-alloy composite extrusion is formed. At 25, the aluminum-alloy composite extrusion may be machined, optionally, to the desired shape. If rolling is selected, then at 26, the aluminum-alloy composite may be rolled to form a sheet. At 28, the rolled sheet may be optionally formed, cut and/or machined into the desired shape. It will be noted that extrusion step 24 and rolling step 26 may be enacted independently of the other or in combination, and in general, each of steps 24 through 28 are optional. Typically, extruded aluminum can be made to near net shape in the extrusion direction, and then machined to a desired shape. Rolled aluminum sheet, by contrast, is typically formed to the desired shape, and may or may not be subject to subsequent machining.

At 30 of method 16, the aluminum-alloy article is anodized. The anodization process may include any suitable cleaning or chemical etching step (e.g., acid or base etching) followed by electrochemical oxidation in a suitable electrolyte solution—e.g., an aqueous sulfuric acid or suitable carboxylic acid solution.

FIG. 3 shows aspects of one example article of manufacture that may be formed according to example method 16. Article 32 of FIG. 3 includes a bulk layer 34 of an aluminum-alloy composite, and a surface layer 36. Bulk layer 34 includes an aggregate 38 dispersed in aluminum-alloy matrix 40. As noted in the context of method 16, the aluminum-alloy matrix may include a 5xxx- or 6xxx-series aluminum alloy or unalloyed aluminum, and the aggregate may include a powdered carbide, nitride, or oxide—e.g., alumina powder. As the aggregate is solid and generally unreactive in the aluminum-alloy matrix (both molten and solidified), the average particle size and the proportion of the aggregate in the bulk layer may be the same as noted above.

Continuing in FIG. 3, surface layer 36 comprises an anodized form 42 of bulk layer 34. In some examples, the surface layer formed by anodization may have a substantially homogeneous—e.g., aluminum oxide—speciation. For instance, if the bulk layer is a composite of aluminum oxide aggregate in a mostly-aluminum matrix, anodization will simply grow more aluminum oxide at the surface and leave the aggregate unchanged. In some examples, the surface layer may be 1 to 30 μm, may present numerous light-scattering centers, and may have a substantially homogeneous, matte appearance. A relatively thick anodized surface layer may be a suitable substrate for a dye or colorant, which may be used in order to impart a desired color to the article. In other examples, the surface layer may be thinner than 1 μm and may exhibit a diffractive optical effect.

Hardened aluminum-alloy articles as described above may be stronger than articles of equal thickness made from unhardened aluminum alloys. This advantage enables the manufacture of strong, lightweight products for a variety of applications. Moreover, the articles formed using the above methods may present an attractive, wear-resistant outer surface, which is desirable in various manufacturing areas.

Another example provides an article comprising a bulk layer of an aluminum-alloy composite, the aluminum-alloy composite including an aggregate dispersed in an aluminum-alloy matrix, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix, and having an average particle size of 100 microns or less; and a surface layer comprising an anodized form of the bulk layer.

In some implementations, the aluminum-alloy matrix includes a 5xxx-series aluminum alloy. In some implementations, the aluminum-alloy matrix includes a 6xxx-series aluminum alloy. In some implementations, the aggregate includes one or more of a carbide, nitride, or oxide. In some implementations, the aggregate includes alumina powder. In some implementations, the aggregate has an average particle size of 20 microns or less. In some implementations, the aggregate has an average particle size of 5 microns or less. In some implementations, the aggregate comprises 1 to 10 percent by mass of the aluminum-alloy composite. In some implementations, the surface layer is 1 micron or greater in thickness. In some implementations, the article is a body of a portable computing device.

Another example provides an article formed from an aluminum-alloy composite, comprising a bulk layer of the aluminum-alloy composite, the aluminum-alloy composite including an alumina-powder aggregate dispersed in an aluminum-alloy matrix, the alumina-powder aggregate having an average particle size of 20 microns or less; and a surface layer comprising an anodized form of the bulk layer.

In some implementations, the aluminum-alloy matrix includes a 5xxx-series aluminum alloy. In some implementations, the aluminum-alloy matrix includes a 6xxx-series aluminum alloy. In some implementations, the aggregate has an average particle size of 10 microns or less. In some implementations, the aggregate has an average particle size of 1 micron or less. In some implementations, the aggregate comprises 1 to 20 percent by mass of the aluminum-alloy composite.

Another example provides a method of manufacture of an aluminum-alloy composite article, the method comprising: melting an aluminum alloy; dispersing an aggregate in the melted aluminum alloy to form a dispersion, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix, and having an average particle size of 100 microns or less; cooling the dispersion to below a solidification point of the dispersion to form an aluminum-alloy composite; extruding the aluminum-alloy composite to form an aluminum-alloy composite extrusion; and anodizing the aluminum-alloy composite extrusion.

In some implementations, the method further comprises rolling the aluminum-alloy composite extrusion prior to anodizing. In some implementations, the aggregate includes alumina powder. In some implementations, the aggregate has an average particle size of 20 microns or less.

It will be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. As such, various acts illustrated and/or described may be performed in the sequence illustrated and/or described, in other sequences, in parallel, or omitted. Likewise, the order of the above-described processes may be changed.

The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various processes, systems and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof. 

1. An article comprising: a bulk layer of an aluminum-alloy composite, the aluminum-alloy composite including an aggregate dispersed in an aluminum-alloy matrix, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix, and having an average particle size of 100 microns or less; and a surface layer comprising an anodized form of the bulk layer.
 2. The article of claim 1 wherein the aluminum-alloy matrix includes a 5xxx-series aluminum alloy.
 3. The article of claim 1 wherein the aluminum-alloy matrix includes a 6xxx-series aluminum alloy.
 4. The article of claim 1 wherein the aggregate includes one or more of a carbide, nitride, or oxide.
 5. The article of claim 1 wherein the aggregate includes alumina powder.
 6. The article of claim 1 wherein the aggregate has an average particle size of 20 microns or less.
 7. The article of claim 1 wherein the aggregate has an average particle size of 5 microns or less.
 8. The article of claim 1 wherein the aggregate comprises 1 to 10 percent by mass of the aluminum-alloy composite.
 9. The article of claim 1 wherein the surface layer is 1 micron or greater in thickness.
 10. The article of claim 1 wherein the article is a body of a portable computing device.
 11. An article formed from an aluminum-alloy composite, comprising: a bulk layer of the aluminum-alloy composite, the aluminum-alloy composite including an alumina-powder aggregate dispersed in an aluminum-alloy matrix, the alumina-powder aggregate having an average particle size of 20 microns or less; and a surface layer comprising an anodized form of the bulk layer.
 12. The article of claim 11 wherein the aluminum-alloy matrix includes a 5xxx-series aluminum alloy.
 13. The article of claim 11 wherein the aluminum-alloy matrix includes a 6xxx-series aluminum alloy.
 14. The article of claim 11 wherein the aggregate has an average particle size of 10 microns or less.
 15. The article of claim 11 wherein the aggregate has an average particle size of 1 micron or less.
 16. The article of claim 11 wherein the aggregate comprises 1 to 20 percent by mass of the aluminum-alloy composite.
 17. A method of manufacture of an aluminum-alloy composite article, the method comprising: melting an aluminum alloy; dispersing an aggregate in the melted aluminum alloy to form a dispersion, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix, and having an average particle size of 100 microns or less; cooling the dispersion to below a solidification point of the dispersion to form an aluminum-alloy composite; extruding the aluminum-alloy composite to form an aluminum-alloy composite extrusion; and anodizing the aluminum-alloy composite extrusion.
 18. The method of claim 17 further comprising rolling the aluminum-alloy composite extrusion prior to anodizing.
 19. The method of claim 17 wherein the aggregate includes alumina powder.
 20. The method of claim 17 wherein the aggregate has an average particle size of 20 microns or less. 